In many gas lasers including many excimer lasers, a gain medium is produced in a laser chamber by a discharge through a gas between two electrodes. For high repetition rates it is normally necessary to circulate the gas so that fresh gas is available between the electrodes at the beginning of each pulse. Often this circulation is provided by a blower with a tangential blower blade structure located inside the laser chamber which is driven by an electric motor and supported by bearings.
For many laser applications laser beam parameters must be controlled to very tight tolerances in terms of pulse energy, beam cross sectional dimensions, wavelength and bandwidth. Vibration, especially at resonant frequencies produced by the blower, can affect laser optical components and degrade laser beam quality.
In line narrowed excimer lasers a well known technique is to mount the laser optics separate from the laser chamber which contains the rapidly rotating blower, with the output coupler at the output side of the laser and a line narrowing unit at the opposite side of the laser. Although mounted separately, both the chamber and the laser optics are typically contained within a laser cabinet and both are mounted on the same laser frame.
U.S. Pat. No. 6,109,574 recently issued on Aug. 29, 2000 describes a support structure including two flexible clamps for isolating chamber produced vibrations in the horizontal direction normal to the direction of the laser beam. U.S. Pat. No. 6,109,574 is incorporated herein by reference. In the patent, the Applicants stated that xe2x80x9cFrame 100 is very stiff in the vertical direction so that the transfer of vertical vibrations from this chamber through the frame elements to the optical components is very small.xe2x80x9d Therefore, no further solution was proposed to deal with the vertical vibrations.
What is needed is a laser support structure to minimize the effects of vertical vibration.
The present invention provides a chamber/optics support structure for a laser having a laser chamber with a vibration source. The chamber and the laser resonance cavity optical elements are supported on a platform. The chamber is supported by a plurality of wheels which in turn rests on two tracks on track supports mounted on the platform. A vertical vibration isolator isolates vertical vibrations originating in the chamber from the laser optics. A flexible clamp flexibly clamps the chamber in a horizontal position to align it with the resonance cavity optical elements and to substantially decouple vibration between the chamber vibration source to the optical elements in a frequency range of concern.
The invention is especially useful for positioning the heavy laser chamber of a narrow band excimer laser and for decoupling vibrations resulting from its blower from the lasers line narrowing module and output coupler. In a preferred embodiment the plurality of wheels is three wheels, two of which rest in a V-groove track and one of which rests on a flat track. This preferred embodiment uses two flexible clamps each having an adjustment bolt and four symmetrically spaced silicon rubber vibration isolators. Precise horizontal alignment of the chamber is accomplished using the adjustment bolt which is then held in position with a lock nut and a clamping bolt. Silicon rubber dampers in the isolators decouple horizontal chamber vibrations from the optical elements.
In specific embodiments, the vertical vibration isolator may be a flexible liner in the wheels or in the rails or alternatively a pad on which the chamber rests.